How to redirect part of standard output from a shell command

Question

I have the below shell commands to generate the ssh key and to add the public key to authorized keys. But, I want to redirect all the out put of this command to a file while I have to get the prompt generated by these commands to enter output.

ssh-keygen -f /home/$cu/.ssh/${ssh_key}_rsa -t rsa -N ''
# Add Public Key to authorized keys
ssh-copy-id -i /home/$cu/.ssh/${ssh_key}_rsa.pub $Linux_User@$Linux_Machine

Could you please provide your suggestions.

Eh? The prompt isn't on stdout at all. A well-written program (and OpenSSH certainly follows these conventions) will prompt either to stderr or direct to the TTY, not to stdout. A prompt for a password, in particular, will go direct to the TTY. — Charles Duffy
– Charles Duffy, Commented Aug 14, 2017 at 17:02
Can you reformulate the question to let someone reproduce the problem you're facing, as opposed to being written in a way that depends on an incorrect assumption? — Charles Duffy
– Charles Duffy, Commented Aug 14, 2017 at 17:04
(By the way, what's the vi tag doing here? I don't see anything in title or text that describes how an editor is involved). — Charles Duffy
– Charles Duffy, Commented Aug 14, 2017 at 17:04
@CharlesDuffy About 5 seconds of checking shows ssh-keygen prompts to stderr. — gbtimmon
– gbtimmon, Commented Aug 14, 2017 at 17:13

gbtimmon · Accepted Answer · 2017-08-14 17:17:39Z

1

The answer you are looking for is probably a command called tee which will split a stream into 2. Although you can get very complicated with it, the most common use is to write something to a file while also letting the streams still print out like normal just like what you are looking for.

ssh-keygen -f /home/$cu/.ssh/${ssh_key}_rsa -t rsa -N '' | tee -a $log_file

ssh-copy-id -i /home/$cu/.ssh/${ssh_key}_rsa.pub $Linux_User@$Linux_Machine | tee -a $log_file

answered Aug 14, 2017 at 17:17

gbtimmon

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Charles Duffy Over a year ago

Aside: Lots of missing quotes here. That's true in the question, too, but ideally an answer should try to showcase good practices.

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